The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Jet fighter's first missile launch trial

The controversial Lockheed Martin F-35 Joint Strike Fighter (JSF) has conducted its first in-flight missile launch in ongoing trials in the United States.

The US Air Force aircraft called AF-1, a conventional take-off and landing version of the same type Australia plans to buy, released the AIM-120 AMRAAM air-to-air missile over a US military test range last week.

The missile, equipped with an instrumental payload rather than a live warhead, successfully fired its rocket motor following launch.

Lockheed Martin says targeted launches will be conducted in trials later this year.

Australia is planning to buy as many as 100 JSF aircraft but has so far committed to just two, which will be delivered in the US next year for initial RAAF flight training.

JSF has been repeatedly criticised for running late, costing too much and being unlikely to deliver all the promised advanced capability.

However Lockheed has recently reported significant progress in flight testing and even a reduction in cost as the multibillion program matures.